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What is the basic principle of the magnetic compass?（）
A:Magnetic materials of the same polarity repel each other and those of opposite polarity attract
B:The Earth's magnetic lines of force are parallel to the surface of the Earth
C:Magnetic meridians connect points of equal magnetic variation
D:The compass needle(s) will，when properly compensated，lie parallel to the isogonic lines of the Earth

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出自：海船船员证

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